1. Technical Field
The present invention relates to a mixed crystal and a colored pigment dispersion composition.
2. Background Art
Phthalocyanine pigments have the greatest production volume among organic pigments, have a broad range of hues from blue to green, are very vivid, have great tinting strength, and have various high fastnesses. In addition, since they are produced with relatively low cost, they are important pigments widely used in coloring fields. Among the phthalocyanine pigments, a copper phthalocyanine pigment is characterized by hue and vividness, and is most suitable for obtaining the color of cyan, which is one of three primary colors in color printing.
The copper phthalocyanine pigment is known to be classified into three types of crystal forms of δ and ε, α and γ, and β, wherein the hue shifts to greenish blue in this order. As described, there is correlation between the crystal form and the hue, and, therefore, the copper phthalocyanine has different applications depending on the crystal form. For example, the ε type is used for color filters and the like, the α type is used for cotton prints, inks, paints and the like, and the β type is used for toners, gravure printing and the like (see, for example, Organic Pigment Handbook, edited by Color Office).
However, as the result of the diversification of technologies, the current circumstances are such that the required hue as a blue pigment can not be expressed by one kind of copper phthalocyanine pigment. For example, the ε type copper phthalocyanine for use in color filters has slightly insufficient reddish hue, and, therefore, it is currently used with Pigment Violet 23 in combination. As described above, some methods for producing a colored composition are known, in which two or more kinds of pigments are mixed to adjust a hue to a preferable region.
For mixing two or more kinds of pigments, mixing of different kinds of pigment dispersions, mixing by sublimation, mixing by reprecipitation, and the like are generally known.
As a technique of mixing different kinds of pigment dispersions, there is mentioned a method of mixing a copper phthalocyanine pigment dispersion and a copper azaphthalocyanine pigment dispersion (see, for example, Japanese Patent Application Laid-Open (JP-A) No. 11-302548). This is a method for improving the transmittance in high quality color filters, particularly, in blue image portions, and is a favorable technique for forming blue image portions suitable for three wavelength fluorescent lamps, that is, highly transparent in three wavelength fluorescent lamps, by mixing both pigment dispersions to control a wavelength that gives the maximum transmittance.
As a method for improving various performances of a dispersion in addition to improving the agglomeration property, a technique of obtaining a mixed crystal by a reprecipitation method is known. For example, a technique is known for improving light durability and weather resistance by an acid pasting method for a quinacridone-based mixed crystal pigment as an automotive paint (see, for example, JP-A No. 62-62867). Further, for a mixed crystal of a quinacridone-based pigment obtained by neutralizing a pigment solution dissolved in a base and an organic solvent with an acid, a technique of controlling the particle size of the pigment is known (see, for example, JP-A No. 60-35055).
Furthermore, a method is known for manufacturing a phthalocyanine mixed crystal body by dissolving a phthalocyanine-based compound selected from hydrogen phthalocyanine, copper phthalocyanine, titanyl phthalocyanine and vanadyl phthalocyanine in an inorganic acid or an alkylsulfonic acid and by allowing the same to precipitate (see, for example, JP-A No. 8-67829). It is said that, by using this mixed crystal body as a photosensitive material, such improvement of a property is achieved that current flows at once down to the ground potential (residual potential) relative to a prescribed input light quantity (referred to as a high γ property) in digital recording with a laser.
Furthermore, such an example as applying a mixed crystal of titanyl phthalocyanine, halogenated metal phthalocyanine having a trivalent metal as the central metal, and a metal-less phthalocyanine as a phthalocyanine compound to an electrophotographic photosensitive material is known (see, for example, JP-A No. 2002-251027). It is said that the use of this mixed crystal body achieves high sensitivity as an electrophotographic photosensitive material.
Furthermore, an example of applying a phthalocyanine mixed crystal of a phthalocyanine having a trifluoromethyl group and including cobalt, nickel or copper as the central metal, and a phthalocyanine that may have a substituent other than a trifluoromethyl group and includes cobalt, nickel or copper as the central metal is known (see, for example, JP-A Nos. 2005-133023 and 2005-134781). It is said that, as the result of this technique, vividness in color filters, that is, the light selectivity of blue filter segments in a photolithographic method, is enhanced.
On the other hand, a method is known for producing a mixed crystal by a sublimation method of different kinds of phthalocyanine derivatives, which is a technique for obtaining an inductive photoconductor for a semiconductor laser (see, for example, JR-A No. 2-84661). In more detail, this is a method in which a copper phthalocyanine pigment and a metal-less phthalocyanine pigment are once foamed into a molecular-state mixture by a sulfuric acid pasting method, and this is heated to the sublimation temperature in a vacuum and deposited onto an aluminum plate. This is an effective method for forming one crystalline body (pigment body) by mixing two or more kinds of phthalocyanines at a molecular level.
The pigment mixtures and pigment mixed crystal bodies described above need, in general, to be treated as a pigment dispersion, and, for the pigment dispersion, for example, such properties are required as (1) expressing intensively reddish blue, (2) being dispersed easily, (3) having good storage stability of the dispersion, and the like.